Thank you for the post. I wonder if you have seen bagged Earl Grey Decaf Green tea? If not, do you have a recommendation as to the best way to use loose? I have seen reusable muslin teabags and metal infuser balls. Do you have a preference?

Caffeine only develops in tea during the oxidation process. A process that black tea goes during its fermentation.

Green tea doesn't have this fermentation process and so its caffeine content is very, very low anyway. You'd probably find little difference in caffeine content between a decaf and non-decaf green tea - if you could find a decaf green in the first place.

Actually Ashiro, that's dead wrong. Only puerh undergoes true fermentation, while oolongs and blacks are oxidized. Anyway, caffeine is not "developed" during oxidation– it's already there in the living plant.

Also, green tea does have a significant amount of caffeine. Perhaps not as much as black tea, but certainly more than decaf.

The extent of processing undergone by black teas is (usually) much higher than anything oolongs, greens, and whites go through. Consequently, black tea leaves are a bit more 'broken up' on the cellular level, which allows those cell contents to infuse into water more readily. I'd bet my car that this accounts for the higher amount of caffeine in black teas, followed by (you guessed it), oolong, green, then white.

Amounts of caffeine can also differ across the many varietals of the tea plant itself, but I would still put my money on the advanced cell rupture of blacks to account for the caffeine in the cup.